Aircraft lavatory systems must be serviced regularly when the aircraft is on the ground. As shown in FIG. 1, aircraft lavatory systems 10 generally include one or more toilet bowls 20 connected to a waste storage tank 40, which stores bodily waste. The waste storage tank 40 is connected to a waste drain fitting (or coupling) 50 by a waste drain tube 30 for discharging waste, and a ground flush (or rinse) line 60 for filling the waste storage tank 40 with sanitizing fluid. Access to the waste drain fitting 50 and ground flush line 60 is provided through a service panel 70 located on an underside of the aircraft, as shown, for example, in FIG. 8.
During routine ground maintenance by ground service crews, the waste storage tank 40 is typically emptied and rinsed, and the sanitizing fluid is replenished. In this way, waste is drained from the waste storage tank 40 via the waste drain tube 30 and waste drain fitting 50, and sanitizing fluid is pumped back into the waste storage tank 40 via the ground flush (or rinse) line 60. The sanitizing fluid is pumped into the water storage tank 40 from a lavatory service truck or cart through a ground flush line connection 80, located in the service panel 70, coupled to the ground flush line 60. For purposes of this disclosure, sanitizing fluid, also referred to herein as “blue fluid” or “blue water,” refers to a fluid with disinfectant chemicals that is mixed with water. This chemical water disinfects and breaks down waste solids.
Ground service crews must be careful not to overfill the waste storage tank with sanitizing fluid or water. When the waste storage tank is overfilled, the blue water or waste may overflow out of the toilet onto carpeting, finished surfaces, or fixtures inside the aircraft. When this happens, waste fluid may get under the floorboards, requiring maintenance personnel to remove floorboards for inspection and replace wiring or other components. There have been instances where ground service crews have overfilled the waste storage tank, causing damage to the aircraft flooring and other components that required the aircraft to be grounded. For example, in one instance a ground crew pumped 100 gallons of water into the water storage tank of a small plane that was designed to hold only 7 gallons of water. This resulted in over $130,000 of property damage, diminished the value of the aircraft by over $800,000, and caused the aircraft to be grounded for several days. Even a small amount of overfill, for example, an overfill of between 1 to 5 gallons could cost up to $40,000 to repair, not including re-inspection fees. Cost to repair larger commercial aircraft due to overfill may be significantly larger. In addition, each hour of down time may cost a commercial airline close to $6,000.
There is presently no industry accepted standard, or preventative hardware or software program for monitoring overfill of aircraft lavatory systems. Some manufacturers of the servicing equipment provide guides and placards to assist the ground crew operators in knowing the proper quantities of fluids to service lavatory systems. However, the procedures must be carefully followed and monitored. Moreover, the ground service crews often comprise new hires that exacerbate the problems. On the other hand, aircrafts must be adapted if new hardware and software are to be installed to avoid overfill problems. The costs are prohibitive.
Absent human errors from ground service crews, components in lavatory filling systems may still fail due to contact with the chemical water overtime. For example, lavatory filling systems often rely on meters that may provide faulty readings, thus causing overfills. Studies have shown that the leading and most costly cause of aircraft lavatory overfill damage is directly related to fluid meter systems. These metering systems commonly use a mechanical wheel or rotating disc-type meters to measure fluid flow. As the fill fluid (i.e., blue water) is pumped through these meters, it actuates the gear, wheel or disc by contact with the fluid. The lavatory treatment additives and/or chemicals added to the fill fluid are somewhat sticky in nature and widely known to damage the metering mechanism. The sticky fluid may case the meter to undercount or not count the fluid being pumped onboard the aircraft. Pumping systems on these vehicles or carts deliver as little as 2 GPM (gallons per minute), and as much as 25 GPM. Therefore, in an example where only 3 gallons of sanitizing fluid is required to be added in a corporate aircraft application, it may only take a minute or two to overfill a waste storage tank.
A need therefore exists for an intermittent fluid delivery system for use in aircraft lavatory filling system that can substantially prevent overfilling, an advantage heretofore unknown in the art.